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1. Field of the Invention
The present invention relates to the assembly and installation of precast concrete segments used in construction activities, such as bridge and highway construction. More particularly, the present invention relates to couplers for joining the ends of interior ducts of such precast concrete segments in end-to-end liquid-tight relationship.
2. Description of the Prior Art
Precast segmental bridges are known and commonly used throughout the world as a means to forge roadways through mountainous terrain or across rivers or other barriers. Such bridges are typically constructed in accordance with the following sequence: First, a series of upright piers are formed along the bridge span. Thereafter, cantilevered bridge section are built out of each pier by successively mounting the precast segments to previously completed bridge components and post-tensioning the segments thereto. The cantilevered bridge sections are built out from each pier in a symmetrical fashion so that the piers are not subjected to undue bending loads. When the cantilevered sections are complete, the ends thereof are post-tensioned together to form a continuous bridge deck. Typically, two such bridge spans are constructed to accommodate the two directions of travel. These spans are generally side-by-side, but need not be parallel (horizontally or vertically) nor at the same elevation.
FIGS. 1-4 illustrate a form of such precast segmental bridge construction in accordance with the teachings of U.S. Pat. No. 5,231,936, issued on Aug. 3, 1993 to G. Sauvagiot. This form of segmental precast bridge construction is particularly disclosed as used with a rapid transit viaduct system.
Referring to FIG. 1, a rapid transit viaduct section two includes a central load bearing span or body member 4 supported by a pair of upright pier members 6 and 8. Extending laterally from opposite lower side portions of the central body 4 are a pair of lateral platform structures 10 and 12. Each of the platform structures 10 and 12 has a pair of rails 14 mounted thereon for carrying a rapid transit vehicle. In addition, each of the platform sections may be provided with an upright sidewall section 16 as required for safety, noise pollution and other considerations. One or more sets of rails 14 are carried by each of the lateral platform structures depending on the requirements of the transit systems.
The platform structures 10 and 12 each include respective upper platform decks and respective lower support struts 22 and 24. The lower support struts 22 and 24 are mounted as close to the bottom of the central load bearing body 4 as practicable. Deck members 18 and 20 are mounted to the central body 4 at an intermediate portion thereof above the support struts 22 and 24. The support struts angle upwardly from their point of attachment with the load bearing body 4 until they intersect the deck members. As such, the deck members 18 and 20 and support struts 22 and 24 form a box section providing resistance to torsional loading caused by track curvature and differential train loading. This box section may be considered a closed base. The load bearing body 4 bisects the closed base and extends vertically upwardly therefrom to provide span-wise bending resistance. Preferably, the entire duct section 2 is cast as a single reinforced concrete cross-section.
The platform sections 10 and 12 each include lower pier mounts 26 and 28. These are mounted respectively to the bottom of the support structures 22 and 24. The pier mounts 26 and 28 are, in turn, supported, respectively, on the piers 6 and 8 using a plurality of neoprene pads 30, which provide a cushioned support for the structure.
As shown in FIG. 1, the viaduct section 2 forms part of a viaduct system supporting rails 14 for carrying rapid transit vehicles 32 and 34. The viaduct section 2 may be formed as a precast modular segment. The viaduct section 2 is then combined with other viaduct sections to form a precast segmental structure. To facilitate such construction, the load bearing body 4 may be formed with interlock member 36, while the lateral platform structures 10 and 12 may be each formed with interlock members 38.
Referring to FIG. 2, a viaduct system is formed from a plurality of precast sections 2 formed as modular segments and combined as a precast segmental structure extending between sequentially positioned piers (not shown). The sections 2 are placed in longitudinally abutting relationship. To facilitate that construction, the sections are match cast so that the abutting end portions thereof fit one another in an intimate interlocking relationship. Each successive section is therefor cast against a previously cast adjacent section to assure interface continuity.
The connection between adjacent modular sections is further secured by way of the interlock members 36 and 38. On one end of each section 2, the interlock members 36 and 38 are formed as external keys. On the opposite end of each section 2, the interlock members are formed as an internal slot or notch, corresponding to the key members of the adjacent viaduct system. Match casting assures that corresponding keys and slots, as well as the remaining interface surfaces, properly fit one another.
As seen in FIG. 2, the sections 2 are bound together with one or more post-tensioning cables or tendons 40, 42 and 44. The number of cables used will depend on a number of factors such as cable thickness, span length and loading requirements. The tensioning cables are each routed along a predetermined path which varies in vertical or lateral position along the span of the segmental structure.
FIG. 3 illustrates, diagrammatically, the manner in which the post-tensioning cables 40, 42 and 44 extend through the concrete structure of the spans. As can be seen in FIG. 3, the post-tensioning cables are sometimes positioned within the concrete segment themselves, and at other times are positioned externally thereof.
It is important to note that multiple post-tension cables are often used as extending through ducts within the concrete structure. In FIG. 4, it can be seen that the sections 2 are formed with appropriate guide ducts 50 at locations where the post-tensioning cables passed through the structure. The post-tensioning cable identified collectively by reference numeral 52 in FIG. 4, are routed through the guide ducts 50. To facilitate this routing, a continuous flexible conduit 54 is initially inserted through the guide ducts, and the post-tensioning cables 52 are thereafter placed in the conduit. The conduit 54 may advantageously be formed from polyethylene pipe but could also be formed from flexible metallic materials. The post-tensioning cables 52 are tensioned using conventional post-tensioning apparatus and the interior of the conduit 54 is cement grouted along the entire length thereof for corrosion protection.
One form of duct that is commercially available is shown in FIG. 5. The corrugated polymeric duct 56 is of a type presently manufactured by General Technologies, Inc. of Stafford, Tex., licensee of the present inventor. As can be see in FIG. 5, duct 56 has a plurality of corrugations 58 extending radially outwardly from the generally tubular body 60. The duct 56 has ends 62 and 64 through which post-tensioning cables can emerge. In FIG. 5, it can be seen that there are longitudinal channels 66, 68 and 70 extending along the outer surface of the tubular body 60. The longitudinal channels 66, 68 and 70 allow any grout that is introduced into the interior of the duct 56 to flow easily and fully through the interior of the duct 56. The longitudinal channels 66, 68 and 70 also add structural integrity to the length of the duct 56. It is important to realize that the duct 56 can be formed of a suitable length so as to extend fully through one of the segments 2 as used in a precast segmental structure.
Unfortunately, when such ducts, such as duct 56, are used in such precast segmental construction, it is difficult to seal the ends 62 and 64 of each duct to the corresponding duct of an adjacent section of the segmental structure. Conventionally, the segments are joined together in end-to-end relationship through the application of an epoxy material to the matching surfaces of the structure. Under such circumstances, it is very common for the epoxy to flow or to become extruded into the opening at the ends 62 and 64 of the duct when the segments are connected in end-to-end relationship. In other circumstances, a grout is pumped through the interior passageway of the duct 56 so as to offer a seal against the intrusion of air and water into the interior of the duct 56. The grout is pumped through the interior of the ducts. Unfortunately, if there is an incomplete connection between the duct 56 and the duct of an adjoining segment of the segmental structure, then the epoxy will leak out into the interface area between the segments and will not flow fully through the entire duct assembly. Once again, an incomplete grouting of the interior of the duct 56 may occur.
It is important to note that in such precast concrete segmental construction, the concrete will slightly warp when matched with the adjoining section. Even though match casting is employed, the lack of homogeneity in the concrete mixtures used for the adjoining sections can cause a misalignment between matching sections. A great deal of tolerance must maintained when a coupler is developed so that any warping or distortion in the surfaces of the matching segments can be accommodated.
The ability to avoid air and liquid intrusion into the interior of the duct 56 is very important in such multi-strand, precast concrete segmental structures. As can be seen in FIG. 1, since the structure is often used on bridges or elevated structures, the post-tensioning cables can be subject to a great deal of exposure from the elements. For example, if the bridge structure is associated with roads traveled by motor vehicles, then there is often the application of salt onto the highway. This salt, when dissolved in water, can leach through the area between the structure segments into the ducts and deteriorate the post-tensioning cables over time. As the post-tensioning cables become corroded, over time, they can weaken so as to potentially cause the failure of the segmental structure. Past experience with such structures has shown that the primary area of leakage would be through those cracks formed between those matched segments. As such, it is particularly important to provide a coupler for use in association with the polymeric ducts which will effectively prevent any liquid intrusion from entering the area interior of the ducts and adjacent to the post-tensioning cables.
It is an object of the present invention to provide a coupler apparatus which allows for the coupling of multi-tendon ducts in precast segmental concrete structures.
It is another object of the present invention to provide a coupler apparatus which automatically adjusts for any misalignments or warpage in the matching concrete segments.
It is another object of the present invention to provide a coupler apparatus which assures a liquid-tight seal between the coupler and the connected duct.
It is still a further object of the present invention to provide a coupler apparatus which is easy to install, easy to use and easy to manufacture.
It is still a further object of the present invention to provide a coupler apparatus which effectively prevents the intrusion of an epoxy into the interior of the duct during the sealing of one structural segment to another structural segment.
It is a further object of the present invention to provide a symmetrical duct coupler which facilitates the ability to manufacture and install the components thereof.
These and other objects of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is a coupler apparatus for use with precast concrete segments comprising a first duct having an end and an exterior surface, a first coupler member extending over and around the exterior surface of the first duct and having a seat opening adjacent to an end of the first duct, a second duct having an end and an exterior surface, a second coupler member extending over and around the exterior surface of the second duct and having a seat adjacent to the end of the second duct, and a gasket received in the seat of the first coupler member and in the seat of the second coupler member. The gasket serves to prevent liquid from passing between the ends of the coupler members into an interior of either of the first and second ducts. The first duct and the first coupler are embedded in a first concrete segment. The second duct and the second coupler member are embedded in a second concrete segment. The seat of the first coupler member faces the seat of the second coupler member.
An external seal is affixed in generally liquid-tight relationship to an opposite end of the first coupler member and is also affixed to the exterior surface of the first duct. This external seal is formed of a heat shrink material. This external seal is in compressive contact with the exterior surface of the first coupler member and with the exterior surface of the first duct.
An internal seal is interposed in generally liquid-tight relationship between an interior surface of the second coupler member and an exterior surface of the second duct. This internal seal is an annular ring of an elastomeric material positioned so as to allow relative movement between the second coupler member and the second duct while maintaining the liquid-tight relationship therebetween.
The seat of the first coupler member is a generally wide slot with an opening facing the second coupler member. Similarly, the seat of the second coupler member is a generally wide slot with an opening facing the seat of the first coupler member. The gasket is fixedly received in the slot of the second coupler member. The seat of the first coupler member has a back surface in abutment with an end of the first duct. Similarly, the end of the second coupler member has a back surface in abutment with the end of the second duct. The gasket is an elastomeric ring having a cross-sectional thickness greater than a combined depth of the seats of the first and second coupler members. The elastomeric ring has a surface tapering in thickness extending outwardly of the slot of the second coupler member. The portion extending outwardly of the seat of the second coupler has a thickness greater than the depth of the seat of the first coupler member.
In the present invention, the first duct, the second duct, the first coupler member and the second coupler member are each formed of a polymeric material.